As many as 10 million Americans over the age of 40 years are at risk for developing glaucoma because of ocular hypertension, but only 2.4 million of these 10 million are estimated to have a >2% annual risk of developing POAG and thus meet the cost-effectiveness threshold to initiating hypotensive treatment. The challenge is to identify the 25% of the "at risk" individuals for whom treatment is indicated from the 75% for whom treatment is not cost-effective. Our prediction model which calculates the 5-year risk of developing primary open angle glaucoma (POAG) in individuals with ocular hypertension is based on the pooled data of the untreated arms (n=1,319 participants) of the Ocular Hypertension Treatment Study (OHTS) and the European Glaucoma Prevention Study (EGPS). This prediction model is available on our interactive "risk calculator" web site which has attracted more than 8,000 unique visitors from 72 countries in less than a year. We would like to increase the predictive accuracy and clinical utility of this risk calculator. No prediction model to date, including ours, gives clinicians and patients evidence-based guidance on the reduction of glaucoma risk at various target IOPs (in mmHg) adjusted for the patient's baseline risk factors (Aim 1). The Specific Aims of the proposed study are: Aim 1. To determine the impact of IOP reduction on the risk of developing POAG. We will also determine whether adjusting IOP for CCT increases the precision of the prediction model for development of POAG. Aim 2. To identify baseline factors associated with follow-up IOP (treated and untreated) in ocular hypertensive individuals. Aim 3. To determine if the predictive accuracy of the existing OHTS/EGPS baseline prediction model for the development of POAG is increased by including information on follow-up IOP level, trend or variability. Translation of research findings into clinical practice will be accelerated by placing a link or PDF copy of publications on our website and by including the calculation of target treatment IOPs on the web-based interactive risk calculator. The analysis dataset will include both treated and untreated groups in OHTS and EGPS, a total of N=2,614 participants with a median follow-up of 5.5 years and 260 cases of POAG. The datasets have already been de-identified and harmonized so that the proposed analyses can be undertaken. The Steering Committees of the OHTS and EGPS have approved the collaborative analyses.